According to a trio of new studies released today, we may only be as old as our blood.

Scientists from Harvard and Stanford are in agreement that feeling younger could be as simple as a blood transfusion. In three separate trials published today, the researchers unilaterally agree that injecting elderly mice with blood from younger mice rejuvenates their brains and muscles and reverses some signs of aging.

"We can turn back the clock instead of slowing the clock down," the director of the Center for Molecular Medicine at the National Heart, Lung and Blood Institute told the New York Times.

Two separate teams of scientists—one at the University of California, San Francisco and one at Harvard—published a series of findings this weekend cataloguing the positive effects of GDF11, a protein found in young blood.

Researchers have been testing GDF11 in mice for years, focusing mainly on its positive effects on the heart. But the results from the most recent studies are dramatic: older mice were able to navigate mazes faster, run longer on treadmills, and demonstrated a better sense of smell. And the reverse appeared to be true as well—young mice injected with old blood had noticeable difficulties afterwards.

After four to five weeks of heterochronic parabiosis, the Science study found that muscle stem cells from the older partners had less DNA damage compared with controls. Their neural stem cells got a boost of activity as well, and they had a greater amount of blood flow in their brains.

Then the researchers switched to pure GDF11 injections. When they gave a new group of aged mice four weeks of treatment, they found that the protein itself gave similar enhancements as shared circulation. There were more stem cells in their muscles to create new tissue, and they performed better on strength and endurance tests than controls given saline. GDF11 treatment also increased the amount of blood vessels in their brains.

Harvard biologist Amy Wavers, who authored both of the Harvard studies published today, said that a "small group of human subjects" appeared to have similar GDF11 protein levels to the test mice but warned that scientists need to conduct more research before they can safely test the transfusions on humans.

Not so, says neuroscientist and author of the third study, Tony Wyss-Coray. The researcher says his new start-up company plans to conduct the first-ever young-blood clinical trial with a group of Alzheimer's patients at Stanford this year.